Two Chinese nationals accused of smuggling biological materials into the United States appeared in court Friday as federal authorities fight to keep them detained in cases they say concern "national security."University of Michigan post-doctoral research fellow Yunqing Jian and Huazhong University of Science and Technology student Chengxuan Han were ordered to remain in federal custody as their separate cases remain ongoing. During the hearing, Han, who is accused of mailing packages containing biological materials to the University of Michigan's laboratory, became visibly emotional and was seen choking back tears when she learned her preliminary hearing had been pushed to a later